This invention relates to a method of optimizing cooling, and balancing capacity, energy efficiency and reliability of a refrigeration system undergoing a process of temperature reduction in a refrigerated space.
In refrigeration of a container for carrying cargo, a refrigeration system is attached to cool a container and hold goods within the container at a target temperature. At any given point in time, the refrigeration system operating conditions are determined by several factors. As an example, the target point or set point temperature, the ambient temperature, the temperature inside the refrigerated container, and the electrical characteristics of the electrical power supply all effect the operating conditions. As these parameters change, so do the refrigeration system operating conditions.
Intermodal refrigeration containers are designed to transport goods upon various modes of transportation while a target temperature is maintained inside the container at all times. This type of refrigerated container is subject to particularly severe changes in all of the above-mentioned parameters.
The process of bringing the temperature of an initially warm load and container to a target temperature for an intermodal refrigerated container must occur under widely varying conditions in the above-mentioned parameters. This initial temperature reduction from an initial temperature to a target temperature is commonly referred to as temperature pull down. The power supply characteristics, target temperatures, and ambient temperature can vary greatly, as an example, from very low to very high temperatures. These varying parameters place special requirements on a refrigeration system for intermodal transport containers. While it is desirable to maximize the energy efficiency, the cooling capacity, and the reliability of the refrigeration system, it is often unrealistic to achieve all of these goals for the fixed configuration of a refrigeration system. Operating limitations are imposed on the refrigeration system by the hardware, refrigerant, and safety specifications. Each of these limitations create additional difficulties in maintaining a universal refrigeration system configuration that would satisfy all array of operating conditions that are typical encountered in a containerized refrigeration system. As an example, the maximum cooling capacity mode might not be very efficient in certain cases. Also, operational (i.g. electrical, etc.) limits may be exceeded during maximum cooling capacity operation.
When the refrigeration system utilizes a scroll compressor, there are limits which are particularly difficult to meet. As an example, the scroll compressors have limits on the motor current, discharge pressure, discharge temperature and suction pressure, all of which must be carefully monitored.
Thus, there is a need to create a method and algorithm for tailoring a refrigeration system to accommodate varying operating conditions while protecting the system from operation outside preset limits.